PALAEOENVIRONMENTAL CHANGES OF THE LATE MIOCENE PUERTO MADRYN FORMATION (PENÍNSULA VALDÉS, ARGENTINA) DETECTED USING SEDIMENTOLOGICAL, PALAEONTOLOGICAL AND ICHNOLOGICAL APPROACHES

ALLENDE MOSQUERA AYLEN; CUITIÑO JOSÉ; CELIS S; PEREZ D.E.; ESPINOSA MARCELA A.

Congreso; 4th Palaeontological Virtual Congress; 2023

© 2023 Palaeontological Virtual Congress

The aim of this study is to reconstruct the palaeoenvironmentalevolution of the lower part of the Late Miocene Puerto MadrynFormation at Punta Buenos Aires (NE Patagonia, Argentina) byintegrating sedimentology, fossil diatoms, macroinvertebrates, andichnology. The 45m-thick sedimentary section was divided into eightintervals separated by different types of stratigraphic surfaces. Marinefossils are abundant and diverse in shoreface to offshore deposits,while two intervals are barren of fossils, and are interpreted as prodeltaand estuarine deposits. Different groups of bivalves dominated bypectinids and oysters, together with bryozoans, brachiopods, andgastropods are documented in sand-prone deposits, along with anichnological association dominated by Helicodromites, Ophiomorpha,Taenidium, Teichichnus, and Thalassinoides, indicating moderateenergy shoreface environments. In contrast, mudstone depositscharacterized by Panopea in life position and abundant Chondrites,suggest lower-energy, offshore environments. At the top of the section,reworked shell fragments, together with Thalassinoides and Skolithosin cross-bedded sandstones, suggest tidal channel deposits. Diatomassemblages are dominated by Paralia sulcata, with the exception ofone sample dominated by the marine genus Pseudopodosira. P. sulcataindicates accumulation in coastal marine environments, whereasPseudopodosira might be reflecting a deeper (offshore) environment.All data indicate that the studied deposits accumulated in a wide rangeof palaeoenvironments, suggesting the occurrence of several relativesea-level variations. It is still unclear why the diatom compositionremains unchanged along so different palaeoenvironments as wellas what factors provoked the intercalation of fossil-barren prodeltadeposits within a fossil rich and diverse succession